Oils derived from plant and animal matter are the source of raw material for many important commercial products. For example, oils from plant materials are extensively used in cooking, in cosmetics, in supplements in therapeutic oils, in essential oils, as carriers for insecticides and fungicides, in lubricants, and in myriad other useful products. Consequently, much work has been done over the years in developing improved processes for extracting oil from such materials.
The most widely used process for removing oil from oil-bearing materials is solvent extraction. In solvent extraction, the oil-bearing material is treated with a suitable solvent, usually the lower carbon alkanes such a propane and butane, at elevated temperatures and pressures, to extract the oil from the oil-bearing material. The resulting solvent/oil mixture is then fractionated to separate the valuable oil from the solvent, which is recycled. There are also teachings in the art that normally gaseous solvents can be used at both supercritical and subcritical conditions.
One such teaching is found in U.S. Pat. No. 5,281,732 to Franke wherein a normally gaseous solvent, such as propane, is used to extract oil from oil-bearing which is maintained at conditions to keep a normally gaseous solvent in liquid form, which is passed through a bed of oil-bearing material. The extracted material is collected and the resulting oil/solvent mixture is passed to a separation zone wherein the solvent is flashed off and recycled and the extracted oil collected. Oils are extracted from a variety of cooked foods, including potato chips, in U.S. Pat. No. 5,525,746, also to Franke.
Further, U.S. Pat. No. 4,331,695 to Zosel teaches a process for extracting fats and oils from oil-bearing animal and vegetable materials. The material is contacted with a solvent, such as propane, in the liquid phase and at a temperature below the critical temperature of the solvent to extract fat or oil from the material. The resulting solvent/oil mixture is treated to precipitate the extracted fat or oil from the solvent by heating the solvent to above the critical temperature of the solvent without taking up heat of vaporization. The extracted residue (shreds) is then treated to remove any entrained solvent, either by blowing it directly with steam, or by indirect heating followed by direct steaming.
Other references that teach solvent extraction of oil-bearing materials, with normally gaseous solvents, include U.S. Pat. No. 2,682,551 to Miller and U.S. Pat. No. 2,560,935 to Dickinson. The extracted material must be further processed to remove entrained solvent in each of these two references.
While prior art extraction processes have met with various degrees of commercial success, there still remains a need in the art for an improved solvent extraction process that is more energy and cost efficient, and which is especially suitable for the processing of temperature sensitive extracted oils derived from certain oil-bearing materials.